ACTH

Adrenocorticotropic Hormone

Hormones

What is Adrenocorticotropic Hormone?

Adrenocorticotropic hormone (ACTH) is a 39-amino acid peptide hormone produced by corticotroph cells in the anterior pituitary gland. ACTH is the principal regulator of cortisol production by the adrenal glands and plays a lesser role in stimulating adrenal androgen (DHEA) and mineralocorticoid production. ACTH is derived from a larger precursor molecule called pro-opiomelanocortin (POMC), which also gives rise to melanocyte-stimulating hormone (MSH)—explaining why ACTH excess can cause skin hyperpigmentation.

ACTH secretion follows a strong circadian rhythm, peaking in the early morning (6–8 AM) and reaching its nadir late at night (11 PM–midnight). It is regulated by corticotropin-releasing hormone (CRH) from the hypothalamus and suppressed by cortisol via negative feedback. Stress, illness, hypoglycemia, and major surgery are potent ACTH stimulators. ACTH is always interpreted alongside cortisol, as the ACTH-cortisol pair determines whether a disorder originates in the pituitary, the adrenal glands, or an ectopic source.

Why It Matters

ACTH is the critical hormone for distinguishing the cause of cortisol abnormalities. In Cushing's syndrome, ACTH determines whether excess cortisol is driven by a pituitary tumor (Cushing's disease—ACTH elevated), an ectopic ACTH-producing tumor (ACTH very high), or an autonomous adrenal tumor (ACTH suppressed). In adrenal insufficiency, ACTH distinguishes primary disease (Addison's—ACTH elevated because the pituitary is trying to stimulate failing adrenals) from secondary/central disease (pituitary failure—ACTH low or inappropriately normal). This distinction dictates entirely different treatment approaches.

Normal Reference Ranges

GroupRangeUnit
Morning (6–8 AM)10–60pg/mL
Late Evening<10pg/mL

Reference ranges may vary by laboratory. Always compare results to the ranges provided by your testing facility.

What High ACTH Levels Mean

Common Causes

  • Cushing's disease (pituitary ACTH-secreting adenoma)
  • Ectopic ACTH syndrome (small cell lung cancer, carcinoid tumors)
  • Primary adrenal insufficiency (Addison's disease—compensatory elevation)
  • Congenital adrenal hyperplasia
  • Physiological stress (surgery, trauma, critical illness)
  • Nelson's syndrome (post-bilateral adrenalectomy pituitary expansion)

Possible Symptoms

  • Skin hyperpigmentation (especially in Addison's or ectopic ACTH)
  • Weight gain with central obesity and moon face (Cushing's)
  • Hypertension
  • Muscle weakness and wasting
  • Easy bruising and thin skin
  • Glucose intolerance or diabetes
  • Mood changes, depression, or psychosis

What to do: Elevated ACTH must be interpreted with simultaneous cortisol. High ACTH with high cortisol indicates ACTH-dependent Cushing's syndrome—further workup includes high-dose dexamethasone suppression test, CRH stimulation test, and inferior petrosal sinus sampling (IPSS) to distinguish pituitary from ectopic sources. Pituitary MRI is performed but can miss small microadenomas. Treatment of Cushing's disease is transsphenoidal surgery. Ectopic ACTH requires localization and treatment of the primary tumor. High ACTH with low cortisol indicates primary adrenal insufficiency requiring glucocorticoid and mineralocorticoid replacement.

What Low ACTH Levels Mean

Common Causes

  • Secondary adrenal insufficiency (pituitary disease, surgery, or radiation)
  • Tertiary adrenal insufficiency (chronic exogenous glucocorticoid use)
  • Autonomous adrenal cortisol production (adrenal adenoma or carcinoma)
  • Exogenous Cushing's syndrome (steroid medications)
  • Hypopituitarism (tumors, infiltrative disease, Sheehan syndrome)

Possible Symptoms

  • Fatigue and weakness
  • Nausea, poor appetite, and weight loss
  • Hypotension (usually less severe than primary adrenal insufficiency)
  • Hypoglycemia
  • Pale skin (loss of ACTH-driven melanocyte stimulation)
  • Absence of hyperpigmentation (distinguishes from Addison's)

What to do: Low ACTH with low cortisol suggests secondary or tertiary adrenal insufficiency. An ACTH stimulation test (Cosyntropin test) is performed: in secondary insufficiency, the adrenals may still respond if the deficiency is recent, but in longstanding cases the adrenals atrophy and fail to respond. Pituitary MRI and evaluation of other pituitary axes (TSH, gonadotropins, prolactin, GH) are indicated. If chronic glucocorticoid use is the cause, gradual tapering rather than abrupt discontinuation is essential to allow the HPA axis to recover. Low ACTH with high cortisol suggests an adrenal tumor producing cortisol autonomously.

When Is ACTH Testing Recommended?

  • When evaluating suspected Cushing's syndrome to determine the source
  • When diagnosing or distinguishing primary from secondary adrenal insufficiency
  • When monitoring patients after pituitary surgery
  • When evaluating hyperpigmentation of unknown cause

Frequently Asked Questions

ACTH follows a pronounced circadian rhythm, with peak levels between 6–8 AM and a nadir around midnight. Morning specimens are standard because reference ranges are established for this time, and morning ACTH is most diagnostically useful—it is when the physiological drive for cortisol production is highest. In primary adrenal insufficiency, morning ACTH is characteristically elevated despite the body's attempt to stimulate cortisol. Conversely, in Cushing's syndrome, loss of the normal circadian rhythm (elevated late-night ACTH/cortisol) is an important diagnostic feature. ACTH is also an unstable peptide that degrades rapidly at room temperature, so specimens must be collected in pre-chilled EDTA tubes and processed promptly.
Cushing's syndrome is the umbrella term for any cause of chronic cortisol excess, while Cushing's disease specifically refers to Cushing's syndrome caused by a pituitary ACTH-secreting adenoma—the most common endogenous cause (60–70% of cases). Other causes of Cushing's syndrome include ectopic ACTH production by non-pituitary tumors (10–15%), adrenal tumors autonomously producing cortisol (15–20%), and exogenous glucocorticoid administration (the most common overall cause). ACTH measurement is the key to differentiating these: elevated in Cushing's disease and ectopic ACTH, suppressed in adrenal tumors, and suppressed with a history of steroid use in exogenous Cushing's.
Exogenous glucocorticoids (prednisone, dexamethasone, hydrocortisone, inhaled/topical steroids at high doses) suppress CRH and ACTH through negative feedback. With prolonged use (typically >3 weeks of supraphysiologic doses), the pituitary corticotrophs and the adrenal cortex atrophy. If steroids are abruptly stopped, the suppressed HPA axis cannot respond to stress, potentially causing adrenal crisis—a life-threatening condition with severe hypotension, hypoglycemia, and shock. This is why steroids must be tapered gradually: reducing the dose slowly over weeks to months allows ACTH secretion and adrenal function to recover. Recovery of the HPA axis can take 6–12 months or longer after prolonged steroid use.

Related Biomarkers

CortisolCortisolDHEA-SDHEA-SulfateAldoAldosterone

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Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Reference ranges may vary between laboratories. Always consult your healthcare provider for interpretation of your specific test results.

Disclaimer: SymptomGPT is not a medical diagnosis tool and does not provide medical advice. Always consult a qualified healthcare professional. If you are experiencing a medical emergency, call 911 immediately.